1. Technical Field
This invention relates to overlay protection plate apparatus and method. In one aspect, the invention relates to overlay protection plate apparatus and method for specialized, set-in-the-ground lighting systems utilized for the purpose of guiding pilots during their approach to an airport runway and during the landing and taxi of aircraft.
2. Background
Conventional lighting fixtures forming part of specialized, set-in-the-ground airport lighting systems are mounted on certain steel containers. The steel containers for these airport inset lights can be one-part or two-part and, sometimes, three-part containers and are set below the surface of runways, taxiways, and other aircraft ground traffic areas. The bottom sections of the containers are sometimes called shallow light bases. The top sections are called fixed-length extensions and are manufactured in different fixed lengths and diameters. Flat spacer rings are installed between the extensions and the lighting fixtures for providing height and azimuth adjustments. These conventional steel containers, in addition to serving as bases for mounting the lighting fixtures, also serve as transformer housings and junction boxes to bring electrical power to the lighting fixtures.
The top portion of the lighting fixtures are installed at a close tolerance, slightly above the pavement surface. Installations of the containers and their lighting fixtures are required on two different occasions. The first is when the runways, taxiways, and other aircraft ground traffic areas are built for the first time. The second is for re-surfacing or re-paving of the runways, taxiways, and other aircraft ground traffic areas. The latter is the most common, i.e., most frequent.
When the airport set-in-the-ground lighting system is installed for the first time, the bottom sections of the containers are generally set in a granular sub-base fill, in holes larger than the container's bottom sections. The granular sub-base fill, which can be one to two feet in height, typically constitutes the entire sub-base of the runway, taxiway, or other aircraft ground traffic area.
Electrical conduit is installed in trenches in the sub-base material and fastened to the containers. Electrical wires are pulled through and into each container, which is set precisely aligned in azimuth and height. The trenches then are filled with concrete, and concrete then is poured under and around the containers to encase and anchor them to the sub-base.
At this point, the top flange (inverted flange) of the bottom section of each container is positioned flush with the surface of the granular sub-base in which the concrete-encased container is set.
A 3/4 inch thick plywood cover and a metal plate on top of it are bolted, with six bolts, to the top flange of each container bottom section. The container top flange has holes drilled and tapped with the same bolt circle as the plywood covers and metal plates. The top flange of the bottom section of each container, with its plywood cover and metal plate bolted on it, is set to the height of the surface of the granular sub-base. The purpose of the plywood cover and metal plate is to prevent debris from falling into the bottom section container and to prevent the container flange from being damaged during runway construction. The FAA (Federal Aviation Administration) designation for the metal plate is "mud plate."
If the runway, taxiway, and other aircraft ground traffic area being built are to be constructed with bituminous material, e.g., such as asphalt, instead of concrete, a shingle or other thin material will be placed on top of the mud plates before the tack coat is applied. Prior to paving, the thin material is removed, and the mud plates are lightly wiped with rags soaked in vegetable oil to facilitate the subsequent removal of the asphalt from its surface.
A first course of asphalt, e.g., such as at a depth of four inches or more, is laid down, burying the mud plates under it. The asphalt then is compacted by heavy rolling machines.
For core drilling to begin, the location of each container center point then must be found. Surveyors find the approximate location of each buried container using transits and previously established reference points. The surveyor makes reference markings on the pavement to indicate approximately where the center point of each container should be found or located. The surveyed center point is required for the precise setting of a core drilling bit.
The electrical contractor then drills one or more two-inch pilot holes to the depth of the top of the mud plate. Through these pilot holes, the contractor can determine how close the surveyed center point is to the container center point, by observing the position of raised concentric circles or raised radial markings on the top of the mud plate.
When the precise container center point is determined, a core drilling is made with a drilling bit one inch larger in diameter than the diameter of the buried container. For example, Type L-868 Class I containers are manufactured, per FAA (Federal Aviation Administration) specification, in three sizes: A, B, and C, with nominal outside diameters of 10, 12, and 15 inches, respectively. The core drilling would be 11, 13, or 16 inches, respectively.
When the core drilling is completed, jack hammers are used to break the core-drilled, compacted asphalt cylinder into smaller pieces. The jack hammer technique makes for hard work, a highly labor intensive consuming chore. As a further drawback, the jack hammering on many occasions damages the mud plate by breaking or bending one or more of its bolts.
After jack hammering, the asphalt around the six bolts of the top flange must be cleaned out by hammer and chisel to permit removal of the bolts. The debris then must be removed to prevent the debris from falling into the container below.
After the bolts are removed, it is still difficult to pry away the plywood cover and mud plate, since the work is done kneeling down, working inside a hole with very little room between the wall of the hole and the items to be removed.
After the plywood covers and mud plates are removed, an extension is bolted onto the bottom container's top flange.
The plywood covers and mud plates are bolted down again, this time onto the fixed-length extensions, thereby bringing the surface of the mud plates flush with the newly laid asphalt surface. The surface is then ready for the second course, e.g., four to six inches thicknesses of new asphalt. Again, as with the previous course of asphalt, a shingle or other thin material will be placed on top of each mud plate before the tack coat is applied. Prior to paving, the shingle or other thin material is removed, and the tops of the mud plates are wiped with a rag soaked in vegetable oil. Altogether, two or three courses of asphalt are laid down and compacted by rolling machines, with each course compacted individually.
Because the core drilling diameter is larger than the diameter of the containers, after the extensions and the lighting fixtures are finally installed, an empty space remains between the extensions to which the lighting fixtures are bolted and the wall of the bore hole.
Each airport paving project may consist of installing hundreds of lighting fixtures and their inset containers.
Runways, taxiways, and other aircraft ground traffic areas deteriorate with years of usage. This creates the need for resurfacing or repaving, i.e., replacing the asphalt of these ground surfaces. Repavement is a much more common, i.e., frequent, occurrence than the construction of new pavements.
If the runway, taxiway, apron, or the like is being repaved instead of being newly built, the process starts by removing the lighting fixtures, any spacer rings, and the extensions from the bottom sections of the containers. Removal is required because several inches of the existing, deteriorated pavement must be removed and milled by high speed roto-milling machines.
Before milling, a plywood cover and mud plate are bolted, by means of six bolts, onto the top flange of the bottom section of the containers to prevent debris falling into the containers and to prevent damage by the milling machines to the top flange of the bottom sections.
Then the pavement surface is milled down to the same elevation as the top of the mud plates. After the roto-milling is complete, the entire area is broom cleaned by brooming machines.
After the roto-milling and broom cleaning of the area, the tack coat is applied. Every mud plate is covered as previously described, with a shingle or other thin material, which is removed prior to laying down the asphalt pavement. Approximately four to six inches thicknesses of asphalt pavement are laid over the mud plates and the plywood covers.
Then the process as previously described (for new construction) is carried out in the same manner for repaving. Surveyors locate each container center point and mark approximate locations on the new pavement. Two-inch pilot holes are drilled to determine more precisely the location of the center points. Core drillings are made, and each core-drilled, compacted asphalt cylinder is removed from the core-drilling by jack hammering. The remaining smaller pieces of asphalt are removed from around the six bolts by hammer and chisel. The generated debris is cleaned out. The six bolts are removed. The mud plate and plywood cover are pried out of the bore hole. Any sheared bolt is drilled out, and the container flange retapped, making it ready to receive the new fixed-length extension and lighting fixture. The core drilling diameter is larger than the diameter of the container after the extension and the lighting fixture are finally installed, and an empty space remains between the extension to which the lighting fixture is bolted and the wall of the bore hole.
Since pavement milling contracts stipulate penalties to contractors for undermilling, i.e., taking off less pavement thickness than specified, contractors protect themselves by setting the roto-milling level as low as can be done safely. In doing so, the bolt heads often are damaged either by rounding them out of shape or by shearing them off or bending them. This situation seriously increases the labor costs an electrical contractor must build into the bid, because of the difficulty of removing bolts with rounded-off heads (a socket set will not work, forcing the use of vise grips or channel locks) or drilling out the studs of bolts that have been sheared off and then having to retap the hole or holes. Removing bent bolts is also a difficult task.
If a runway, taxiway, or other aircraft ground traffic area being built is to be constructed with concrete instead of asphalt overlaid on top of the granular sub-base, the containers (whether of a one section or multiple section type) would be set to their final height from the beginning, rather than setting them to the elevation of the surface of the granular sub-base.
This is because the concrete, whether poured in one layer or in several layers, does not require compaction by rolling machines as does asphalt.
The plywood covers and mud plates are installed to prevent having concrete enter into the container itself or into the drilled and tapped bolt holes. The concrete is poured over the height of the mud plate because, as previously described, when the lighting fixtures are installed, a portion of each fixture will be inset to keep its top side slightly above the final surface. Therefore, a portion of each lighting fixture will be under the final surface, but its top will be slightly above it.
Each mud plate thus is covered with concrete and has to be found. Location of the mud plate is simple in this case compared to asphalt because the concrete on top of the mud plate is much thinner than the concrete surrounding the rest of the container. As a result, the thinner concrete cures faster, showing a round spot of a different shade or color than the rest of the surrounding surface. All such containers are in a straight line and are readily locatable, as are their center points.
For the concrete installations, since the concrete above the mud plate is very thin, a cookie cutter is placed in the concrete, from a bridge, while the concrete is still soft. The diameter of the cookie cutter is larger than the diameter of the container below. By doing this, in concrete installations, there is no need for core drilling.
The hardened concrete is chiseled out, e.g., by hammer and chisel and breaks up easily. This chiselling is done to provide access to the six bolts on the mud plates to unbolt and remove the mud plates and plywood covers for installing the lighting fixtures and for the adjustment of their height and azimuth.
The main function of the 3/4 inch thickness plywood covers in this application is to cushion the impacts of the hammer-chiseling from acting directly against the top flange of the container extension and damaging it.
The mud plate and plywood cover constitute the existing art. There are many costly problems and drawbacks associated with the utilization of conventional mud plates and plywood covers in conventional or prior art methods. One problem is the expense involved in using surveyors and transits to find the center point of the mud plates and mark them on the newly laid pavement.
Another drawback is the requirement for drilling one or more two-inch pilot holes to verify that the center point, as marked by the surveyor, is the exact center point of the mud plate, and to provide the necessary precision for centering the core drilling machine.
A further drawback is the requirement for jack hammering out the core-drilled, compacted asphalt cylinder, after the core drilling is done to remove the core-drilled asphalt cylinder from the top of the mud plate. The many pieces of asphalt pavement created by the jack hammering must be removed and the debris loaded up on a truck, container site by container site. Hammering and chiseling out of smaller pieces of asphalt stuck to the six bolts are difficult tasks, including but not limited to doing it while kneeling down over the bore hole.
Another drawback is cleaning up all the small pieces chiseled out and removing them from the bore hole and from the aircraft traffic area.
The conventional methods result in bolts with rounded-off heads, sheared-off heads, or bent bolts, resulting from roto-milling or jack hammering. Therefore, another drawback is dealing with such bolts while kneeling down over the bore hole, by drilling studs and retapping bolt holes, or by removing the six bolts even when none are damaged.
It is also a drawback of conventional methods in the requirement for prying-out both the mud plate and the plywood cover, while kneeling down and with very little space between the edge of the mud plate and plywood cover and the wall of the bore hole.
Therefore, it is an object of the present invention to provide an overlay protection plate apparatus and method which eliminate the need to utilize surveyors for finding the center points.
A further object of the present invention is to provide an overlay protection plate apparatus and method which eliminate the need for drilling two-inch pilot holes.
It is yet another object of the present invention to provide an overlay protection plate apparatus and method which eliminate the need for jack hammering to remove the core-drilled asphalt cylinder.
Another further object of the present invention is to provide an overlay protection plate apparatus and method which eliminate the need for installing plywood covers.
Yet another further object of the present invention is to provide an overlay protection plate apparatus and method which eliminate the need to remove the many smaller pieces of fragmented asphalt from the bore hole for loading onto trucks.
It is a still further object of the present invention to provide an overlay protection plate apparatus and method which eliminate all the problems associated with the bolts.
Also a further object of the present invention is to provide an overlay protection plate apparatus and method which eliminate the need to pry out the plates.
These and other objects of the present invention will become apparent to those skilled in the art from a careful review of the detailed description which follows.